<VV> License Plate Question

[Paul Siano]

I am about to install a new license plate light.  The hot lead goes to the bottom of the bulb.  To complete the circuit, is it necessary to ground the the assembly that mounts to the deck lid?  Currently it is painted. Do I need to sand that area to provide a ground?
What should the surface look like between the the lid and the bulb holder...painted or bare?  Is there some other way the ground is accomplished?

Paul Siano
Lecanto, FL